Electric discharge heat treatment of metals in electrolytes



3, 1965 KIYOSHI INOUE 3,198,675

ELECTRIC DISCHARGE HEAT TREATMENT OF METALS IN ELECTROLYTES OriginalFiled Aug. 15. 1960 5 Sheets-Sheet 1 F/GJ F/G-Z 70 I l4 4 I 2r 1/ T l2 0VCONSTANT' I i k/YOSH/ INOUE INVENTOR BY A 3, 1965 KIYOSHI INOUE3,198,675

ELECTRIC DISCHARGE HEAT TREATMENT OF METALS IN ELECTROLYTES OriginalFiled Aug. 15, 1960 5 Sheets-Sheet 2 FIG. 7

WHEAT/Ne LAMP UNIT D/RECT VOL 7/: as SOURCE K/YOSH/ INOUE INVENTOR.

1N, ,AG NI ELECTRIC DISCHARGE HEAT TREATMENT OF METALS IN ELECTROLYTES 5Sheets-Sheet 3 Original Filed Aug. 15, 1960 FIG. 70

DIRECT VOLTAGE 5 UR n M P. M M 8 2 0 I. M W, w K 0m M N C M 0 mm llll IJ0 w 4 w 1 m 6 n a m W 4 6 M m m o 0W8 8 iL/ fl |l\ m Aug. 3, 1965KIYOSHl lNOUE 3,193,675

ELECTRIC DISCHARGE HEAT TREATMENT OF METALS IN ELECTROLYTES OriginalFiled Aug. 15, 1960 5 Sheets-Sheet 4 DIRECT VOLTA 65 SOURCE FIG. 13

' Howl/v6 MAGNETS D/RECT V01. T4 65 SOURCE Kl YOSH/ INOUE INVENTOR.

" AGENT 3, I965 KlYOSHl INOUE 3,198,675

ELECTRIC DISCHARGE HEAT TREATMENT OF METALS IN ELECTROLYTES OriginalFiled Aug. 15. 1960 5 Sheets-Sheet 5 DIRECT V01. T4 GE SOURCE FIG. 15

K/YOSl-l/ INOUE INVENTOR United States Patent 3,193,675 ELEETRECDEEEEHAEGE HEAT TREATMENT OF METALS IN ELECTRULYTES lliiyeshi inane, 182Yoga Tamagawa Setagaya-hu Tokyo, Japan Griginal application Aug. 15,1960, Ser. No. 49,625. Divided and this application Earn. 2, 1963, Ser.No. 256,790

8 Claims. (Cl. 1143-43) This is a division of application Serial No.49,625, filed August 15, 1960, now abandoned.

This invention relates to improvements in the art of heating metalobjects by creating an electric discharge at the surfaces of the objectimmersed in an electrolyte solution. The invention is hereiniilustratively described by reference to the presently preferredembodiments thereof; however it will be recognized that certainmodifications and changes therein with respect to details may be madewithout departing from the essential features involved.

Among the numerous useful applications for this general heatingtechnique may be listed tempering, annealing or other heat treating ofmetal objects, thermal fabrication (viz. pressure forming or meltiu andmolding of metal), disinfecting of surgical instruments and the like,melting of metal objects such as in the manufacture of metal alloys,etc. The basic principle inherent in the process of heating metalobjects in an electrolyte by an electric discharge process is disclosedin Electrical Review, Februray l, 1929.

Chielly the present invention is concerned with apparatus and methodimprovements which so increase the eificiency and effectiveness of thebasic process as to render the same commercially feasible andversatilely practicable for a number of useful applications heretoforeundeveloped.

Furthermore this invention provides more reliable and consistent resultsthan heretofore, especially in heat treating, and affords new and usefulmeans and techniques of control to that end. The invention also providesautomatic control arrangements and apparatus by which the basictechniques are adaptable to various production appiications.

Another object is to provide a technique and apparatus for heat treatingwherein the heating and subsequent cooling steps are performed rapidly,systematically and without separate handling of the object. In thisregard, the object is both heated and immediately cooled in the sameapparatus, indeed in the same liquid medium. Consequently certainapparatus simplifications are attainable along with better and moreconsistently reliable results.

A specific object is to provide an apparatus and technique whereinenergy consumed in electrolysis and in unstable discharge at the objectsurfaces both during and upon completion of immersion of the object areheld at a minimum. Higher electro-thermal erhciency in the process,lesser metal erosion and reduced consumption of electrolyte are therebyattained.

A further object is to provide a technique and a means for increasingenergy transfer to the electrolytic heating cell on a controlled orautomatic basis, predetermined as to amount and in accordance withrequirements of efficiency.

A related object is to determine and provide electrolyte solutionyielding much higher efiiciency than heretofore.

A specific object hereof is a technique and means by which, usinginsulating topping liquid on the electrolyte liquid, heat is conserved,and related arrangements may thereby be provided for progressivelyheating and cooling metal objects by moving them, either in rotation orin translation along a prescribed path into and through the electrolyteand thereupon into and through the insulating liquid. Consequently theprocess may be applied to uninterrupted rapid-production heat treatmentinasmuch as it becomes possible to cool the heated objects in the liquidenvironment without removing the electrolyte voltage.

Still another specific object is to provide an efficient and reliablemetal molding or forming apparatus wherein the electrolytically heatedmetal objects may be subjected to forming pressures or may be melted andmolded while immersed in the electrolyte and which being held at formingtemperatures therein. Thus thermoforging or casting may be performed inessentially one operation with resultant economies. Other specificobjects include an efiicient and practicable alloy manufacturingapparatus by which alloys, free of oxidation and atmosphericcontamination, are formable in any of dilferent predetermined ingot (orutilitarian) shapes and sizes and with controlled cooling in a liquid(electrolyte) medium inherent to the melting process itself.

These and other obiects along with the novel features and advantages ofthe improvements comprising this invention will become evident as thedescription proceeds with reference to the accompanying drawings.

FIGURE 1 is a simplified and partially schematic side view showing of abasic apparatus arrangement for practicing electrolytic electricdischarge heating.

IGURE 2 is a graph showing discharge current as a function of voltage insuch apparatus.

FIGURE 3 is a graph showing discharge current as a function of time, ata given voltage, in such apparatus.

FIGURES 4(A) and (B) are enlarged and exaggerated sectional viewsdepicting a discharge phenomenon occurring in such apparatus.

FIGURE 5 is a graph showing the voltage and current relationship in anelectrolytic heating cell at different electrolyte temperatures with agiven electrolyte and work surface exposed to the electrolyte.

FIGURE 6 is a graph showing the current and voltage relationship in anelectrolytic heating cellusing a conventional electrolyte and, bycomparison, an electrolyte representing one aspect of the presentimprovements.

FIGURE 7 is a simplified side view of a work heating system illustratingcertain features of the invention.

FIGURE 8 is a graph showing the variation of current llow through theelectrolytic cell as a function of time in the operation of theapparatus shown in FIGURE 7.

FIGURE 9 is a simplified side view of mechanical aspects of a more fullyautomated heat treatment apparatus according to this invention; andFIGURE 10 is a schematic diagram of the related electrical andelectromechanical system of such apparatus.

FIGURE 11 is a simplified side view of heat treating apparatus forapplication to annular or similar work objects which are rotatablymountable; and FIGURE 12 is a plan view thereof.

FIGURE 13 is a simplified side view of heat treating apparatus applyingthe principles of the apparatus of FIGURES 11 and 12 to processing acontinuing succession of articles on a production basis; and FIGURE 14is a plan view thereof.

FIGURE 15 is a simplified side view of heat-forming apparatus employingfeature of the invention.

FIGURE 16 is a simplified side view of heat steriliz ing apparatuembodying features of the invention.

FIGURE 17 is a simplified side view of metal casting apparatus employingthe invention, in this case to manufacture cast alloys.

Further studies and experiments with electric discharge heating throughan electrolyte have revealed certain principles and characteristics outof which have come certain conceptions and discoveries represented inthe present improvements. When an electrically conductive work piece ormetal object W is immersed or partially immersed in an electrolyte E ina container 10 having an opposing electrode such as the conductive liner12 and voltage is applied from a direct voltage source 14, with theobject W connected to the negative side and the liner electrode 12 tothe positive side discharge current will flow through the electrolyte.An ammeter A connected in series and a voltmeter V connected in shunt inthe external circuit measure the cell current i and the applied voltagev. Current flow may be varied by a series-connected variable resistance16. Certain relationships and characteristics are then observable in thesystem.

For instance, as depicted in FIGURE 2, when voltage is increased fromzero progressively through a range of values, as by reducing the size ofresistance 16, current i initially rises at a substantially linearlyproportional rate. A point a is ultimately reached at applied voltage vat which any further progressive increase of voltage causes aprogressive reduction of current, until a second point b is reached.Thereupon a further increase of voltage causes a further increase ofcurrent, although at a somewhat lesser rate of increase than thatoccurring in the first stage. The cresting of the current characteristicof such a cell is explainable from the ionic reactions producing anincreasing insulative blanketing of gas molecules on the work surface aselectrolysis current is progressively increased. Eventually (at point a)the increasing blanketing is sufiicient to progressively reduce thecurrent flow as voltage further increases. This repre sents a secondstage of the current characteristic, between points a and b. At point bthe flow of electrolytic current a such is virtually cut off by theinsulating gas layer.

The ultimate stage, i.e., beyond point b, represents still anothercondition and the one of particular interest herein. Current i willagain start to increase as voltage increases due to the fact that theescaping gas, not now being replenished, leaves localized areas of thework surface exposed directly to the electrolyte. Current flow will thenbe concentrated in these areas, producing intense heat and consequentvaporization of electrolyte. Initially these randomly distributed areasare relatively large and occur infrequently, but as the process isextended farther along into the ultimate stage beyond point b through afurther increase of voltage more and more areas of smaller and smallersize occur. The significacant phenomenon now occurring is that in thisultimate a and the presently useful stage of the current characteristic,current flows through the vaporized electrolyte not largely as anelectrolytic current but primarily as a gaseous electric discharge andheats the entire work piece, the vapors being constantly replenished andbeing additive to the gaseous blanket formed by electrolysis in formingthe insulative blanket. Moreover the heating discharge condition beingdescribed is stable, whereas that occurring in the first and secondstages, to point b, is essentially unstable.

As shown in FIGURE 3, there is also a time factor to be considered inthe process. When a constant area of the Work piece is first exposed tothe electrolyte at a constant applied voltage selected at a value whichwill produce ultimately a discharge condition in the stable dischargestage or heating region (i.e., beyond point b in FIGURE 2) there is atime lag in reaching a stable or quasi-stable condition. First thecurrent i rises very rapidly to a certain value determined by theelectrolytic cell resistance, whereupon it levels off for .a time.During this time the gas blanket builds up until, at time t itsincreasing insulating effect causes a progressive decrease of current.This decrease continues until, at time t the now-reduced electrolyticcurrent, hence the reduced generation of blanketing gas is insufiicientto fully replenish the gas coating in areas as the gas escapes, so thatcurrent flow now levels off and even slightly increases due to thegaseous-electric discharges occurring increasingly in these differentexposed areas on the work piece Referrinng to FIGURE 4, something of thephenomena occurring during the unstable and stable discharge stages(i.e., in FIGURE 2 from a to b and from b on, respectively) may beappreciated which influence the choice of electrolyte. In this figurethe gaseous blanket or layer F made up of electrolytically generated gasmolecules is breached in localized areas and the electrolyte flows intocontact, as at B (FIGURE 4A), with the exposed surface of work piece W.As previously indicated this gives rise to concentrated current flow andintense heating, producing vapors of the electrolyte solvent (usuallyWater) and an ensuing gaseous discharge D (FIGURE 43). An electrolyte ofhigh viscosity and high pecific gravity less readily surges through thebriefly formed gap or break in film F than one of low viscosity andspecific density, in order to reach the Work piece surface. Also, thesmaller the cross section of the contacting finger of electrolyte B, thelarger the current density therein when the contact is formed, at agiven applied cell voltage and electrical resistivity of theelectrolyte. In other Words, for a given total current flow through theelectrolyte to the total work piece immersed therein, the higher theelectrolyte viscosity the lower the applied voltage can be, and therebythe lower the power requirement, in order to attain a certan heatingtemperature.

It will further be seen that the energy supply in the evaporation stagein area B preliminary to producing discharge D is almost wholly consumedin producing evaporation, and contributes little to heating the workpiece. The ensuing electric discharge D creates the heat, Moreover, thevoltage drop along the di charge, hence the amount of heat thusgenerated is virtually independent of discharge gap length, i.e., gasfilm thickness, due to the well known characteristic of a gaseouselectric discharge generally.

Through the foregoing analysis, which has been experimentally verified,it will be evident that the properties of the electrolyte determine thethickness of the gas blanketing film F and consequently the supplyvoltage necessary in order to produce a given value of current. Thus, itwill be recognized that the amount of energy required to bring theheating cell through the initial electrolysis stage i.e., from currentequals zero to point a (FIGURE 2), and through the unstable dischargestage, i.e., from a to b, to the stable discharge stage where heating isdone as a function of electrolyte viscosity and resistivity. The greaterthis energy requirement, the lower the heating etficiency. In order tominimize this energy loss the electrolyte should have a high viscosityand a low electrical resistivity.

Temperature of the electrolyte is also found to be a factor indetermining heating efficiency of the apparatus. Referring to FIGURE 5,the effects of temperature on the interrelationship between cell voltageand current are illustrated. The two graphs represent the example ofpotassium acetate working at 30 C. in one case and at C. in the othercase. Heating the electrolyte to 90 C. proved to reduce the powerconsumption during the non-productive electrolyzing stage toapproximately half that when the electrolyte was maintained at slightlyabove room temperature, i.e., 30 C., with other conditions remaining thesame.

In accordance with one feature and aspect of this invention thepreferred electrolyte for the process is potassium acetate (CH CO0K)solution This compares with known electrolytes heretofore used in theprocess, such as sodium carbonate solution, as shown in FIGURE 6. Fromthis graph it will be seen that a thermal cfficiency with potassiumacetate of thirty to forty percent is attainable, which is from two tofive times higher under worl 0.) ing conditions than that realized whensodium carbonate is used.

Another feature reside in the novel technique for correspondinglyincreasing the thermal efficiency even with formerly used electrolytes,such as sodium carbonate. This is achieved by adding gelatine or starchso as to materially raise the viscosity of the electrolyte. It isfurther improved by adding and mixing into the solution powderedconductive material in sufiicicnt quantity to materially lower theelectrical resistivity.

Still other features will be evident in the basic apparatus embodimentde icted in form and mode of operation in FIGURES 7 and 8.

In FEGURE 7 the work iece W is suspended on a meltable wire 2% from thevertically disposed and movable gear rack 22 guided in a stationarysupport 24 and actuated for vertical movement therein by the pinion 26which is rotated on a fixed support 28 by means of the operating lever3d. The negative side of the voltage source 14 is connected at 32 to thelower end of the rack 22. The positive side of source 14 is connectedthrough the adjustable resistance 34-, by-passed by the switch 36, tothe electrode 12. comprising a liner for the electrolyte container, at38.

The surface of the electrolyte in the container is heated, such as bymeans of the infrared lamp 4-6, to an elevated temperature at least ashigh as in the range between 70 C. and 160 C. Below its heated surfacethe electrolyte is kept at a substantially uniform reduced temperatureby circulating it through a cooling heat exchanger 42 comprising theseparate container having within it a cooling coil 44 suitably suppliedwith cooling fluid from a source not shown. As the electrolytesurrounding the work piece W becomes warm it is drawn oil. by convectionthrough the outlet pipe 46 into the cooling chamber 42 wherein itencounters the cooling coil 44 and, by convection, settles in thecontainer 4-2 and eventually returns through the passage 4-8 to theelectrolyte cell it). Flow of coolant to the coil 44 is controlled so asto maintain the temperature within the cell it) at the appropriate valuefor cooling the work piece W for heat treatment purposes, following itsheating by means of the discharge process. In other words, theelectrolyte E is maintained at the requisite tempering or coolingtemperature, and this may be done by suitable automatic control whichdetermine the flow of coolant to the coil 44 or which, if necessary,increase or decrease the rate of circulation of the electrolyte throughthe heat exchanger 42, or otherwise. Such temperature control is readilyaccomplished by any of different known techniques.

Normally the switch 36 is in the open position. The value of resistance34 is set, by adjusting the slider 34a, so that the voltage appliedbetween the' work piece W and opposing electrode 12 from the source 14,taking into account the voltage drop incurred in the resistance 3 willbe sufiicient to carry the process of discharge through the initialelectrolysis stage and also preferably through the unstable dischargestage (i.e., to point I) in FIGURE 2). However, the voltage should notbe so high that any part of the work piece in process of being loweredor immersed in the electrolyte is heated to a temperature higher thanthe required heating temperature for the entire work piece when it isfully immersed in the final or ultimate heating operation for heattreatment purposes. The deliverable voltage of source 14 itself ischosen so that with the switch 36 closed and the resistance 34 thusbypassed, the resultant flow of current through the cell will heat thework piece to the required temperature for heat treatment purposes, withthe work piece fully immersed.

With the apparatus ready for operation, the handle 30 is turned in theproper direction in order to lower the work piece W gradually into theelectrolyte bath E. FIGURE 8 illustrates the attendant variation of cellcurrent as a function of time. Initially the current i increase rapidly,approximately in proportion to the increase of surface area beingpresented to the electrolyte. The increase of current will terminatevery quicky and the curve will crest and advance into the unstabledischarge region between points a and :5 if the surface area thuspresented is small. The same will happen even with a relatively largesurface area when the surface of the electrolyte is heated to acomparatively high temperature as described previously. Thus, if thesurface of the electrolyte is preheated, as by means of the infraredlamp the creasting current i will be only one-third to onehaif as muchas it would be without preheating, thereby conserving energy inadvancing the process to the final or stabilized heating dischargestage.

When the unstable discharge stage terminates as at time t the currenthas decreased to the value i at point I; and further lowering of thework piece into the electrolyte, exposing larger surface areas thereof,will result in increased current flow until the time i is reached whenthe w rk piece is totally submerged in the electrolyte. At this point te current curve levels out and will remain stable at the value i Then,or at a later time, such as time 1 the switch 36 is closed, therebyby-passing the resistance 34 and applying the full voltage of source 14to the cell. The current will then rise abruptly to the value I; andwill remain at this value while the work piece is heated to thenecessary temperature for purposes of the process.

It will be noted that a part of the suspension wire it is also immersedin the electrolyte E. This portion of the wire is thus heated in thesame manner as the heating of the work piece and, by proper choice ofwire material and cross section, melts through at the appropriate timein order to drop the work piece W into the electrolyte for purposes ofcooling. This is designed to occur when the work has reached the propertemperature for heat treatment purposes, and since the cooling processimmediately follows, the total heat treatment process is accomplished ina very short period of time. As previously mentioned, the temperature ofthe electrolyte maintained by the heat exchanger d3 is established atthe proper reduced value, which is substantially below that of theelectrolyte surface layer, for the cooling phase of the heat treatmentprocess. When the work piece drops into the electrolyte, the current isswitched off by disconnecting the source 14.

Referring to the embodiment shown in FIGURES 9 and Eli, parts whichcorrespond to those in preceding figures bear similar referencecharacters. Work piece W is held on supporting rack 22; by theelectromagnet 5% for lowering the work piece into electrolyte E andsuspending it there while being heated. Motor 52 drives pinion 26 toraise and lower the rack and electromagnet. Lower and upper limitswitches 54 and 56 connected in a control circuit to be described andactuatable by an arm 58 on rack 22 for establishing the vertical travellimits of the rack and electromagnet. Motor 52 is of the reversibledirectcurrent type energized by transformer-rectifier unit 60 through areversing circuit comprising the pair of switches of relay 71 in onebranch, and the pair of switches 74b and 740 of relay 74 in anotherbranch of the circuit. Adjustable, speed control resistance 62 in thefirst-mentioned branch reduces the motor energizing current to asuitable value for lowering the work piece W into the electrolyte at acontrolled rate, whereas the rack and electromagnet are permitted to beraised rapidly by full energization of the motor. The motor 52 moves therack 22 downwardly when relay '71 is energized to close its contacts,and upwardly when the contacts 74b and 740 are closed throughencrgization of relay '74.

Electrornagnet 54% is energized by closure of switch 64, with switch 73cof deenergized relay 73 in its normally closed position.

Heater 4t functions when switch 66 is closed, connecting it totransformer-rectifier unit 60.

Primary source terminals 68 are connected to a threeareaszs phase energysource (not shown). A master switch 7i) in the supply leads controlsapplication of power to the entire system. When this switch is closedA.C. energy is delivered to transformer-rectifier unit 69 as well as tothe relay circuits.

Relay 6?, energization of which is required in order to operate thesystem, is connected across supply leads 78 and 8%) through normallyclosed push-button stopping switch 552 and normally open push-buttonstarting switch 84, when the latter is momentarily pressed closed. Timer73 is connected across supply leads 78 and 556 through normally openswitches 67b of relay 67 and normally closed limit switch 54. Inasmuchas normally open switch 67a of relay s7 is then closed, as is switch 73aof timer 73, and these two are connected in series across switch 84,they thereby form a holding circuit for both the relay 67 and timer 73,so that the complete cycle of the timer 73 will then be self-executingonce it is initiated (i.e., when limit switch 54 is closed).

Relay is connected in parallel with timer 73, hence serially with relayswitch 67b and limit switch 54 across supply leads 78 and 8t Relay 71 isconnected serially with normally closed relay switch 72a and relayswitch 67b across these supply leads. It will therefore be seen thatrelay switch 67b determines the action of the coils of relays 71 and 72and of timer '73. Relay 71 is energized when relay 67 is energized(i.e., with the rack in its raised position). Only when limit switch 54is actuated to the closed position in the downward movement of the rack22, are the coils of relays 72 and of timer 73 energized. When thisoccurs, the opening of relay switch 72 deenergizes relay 7i and therebyopens the energizing circuit of motor 52. The rack movement is therebyterminated with the work piece immersed in electrolyte E. The finalheating period is then initiated.

This heating period (i.e., from t to t in FIGURE 8) is terminated bytimer 73. Completion of the timer cycle results in opening of timerswitches 73a and 730, and closing of timer switch 73b. This causescertain events in the system: (1) The electromagnet 50 is deenergizedand the now heated work piece drops freely into the electrolyte forcooling purposes (i.e., tempering, annealing, etc); (2) the relay 67 isdeenergized, as is timer 73; (3) relay '74, energized through themomentarily closed switch 731) of timer '73, has now formed its ownholding circuit through its holding switch 74a and the normally closedupper limit switch 56, connected serially across supply leads 78 andSi); and (4) the motor 52 is now energized for movement in the reversedirection through the closed switches 74b and 740 of relay 74 to raisethe rack 22 and holding magnet 5%. When the rack reaches its elevatedposition switch 56 is opened by arm 53, deenergizing relay 74 andthereby motor 52. The system is now restored to its original conditionfor a succeeding operating cycle which, as previously mentioned, isinitiated by pressing push-button switch 34.

If at any time during the automatic cycle of operations it is desired tostop the operation, push-button switch 82 may be pressed, deenergizingrelay 67.

Electrolyzing and heating power for operating the cell is produced bythe direct-current generator 90 driven by the motor 92. The generator9t] has a field winding 94 which is energized by the motor-driveneXciter 96 having its own excitation field 98. The generator fieldwinding 94 is connected directly across the eXciter armature 96 whereasthe exciter field winding 98 is connected across the eXciter armaturethrough the two adjustable series resistances 100 and 102 and the switch670 of relay 67. Resistance 100 is connected to the switch 72b of relay72 to be by-passed by closure of this switch when the relay 72 isenergized.

Normally relay switch 670 is opened so that no voltage is generated andthereby none is applied between the work piece W and liner electrode 12.Consequently, mere closure of master switch 70, which starts the motor92,

does not apply voltage to the cell, However, when pushbutton switch 84is pressed, energizing relay 67 and closing relay switch 67c, reducedexciter voltage applied to the generator field 94 through the two seriesresistances and 102 produces an initial electrolyzing voltage across thework piece W and the electrolyte E. This occurs at the same time therack motor 52 is energized to initiate lowering of the work piece intothe cell. The ensuing sequence of events including the variations ofcurrent fiow through the cell represent the successive phases depictedfrom time=0 to time=t in FIGURE 8. At time t represented in this case byactuation of the lower limit switch 54 and initiation of the timingperiod of timer 73, relay 72 is energized. Because relay switch 72a isconnected serially with the motor control relay 71, when relay 72 isenergized relay 71 is deenergized so as to terminate motor operation.Because relay switch 72b is connected across resistance 100 the latteris by-passed so as to apply full excitation voltage to the generatorwinding 94 and thereby full heating voltage to the cell when relay 72 isenergized by the timer 73 at the end of the latters cycle. Resistance102 is adjusted so as to cause the correct value of excitation of thegenerator winding 94 to produce the desired heating voltage. By the sametoken, resistance 100 is adjusted so as to produce the desired initialelectrolyzing voltage for application to the cell during the initial(i.e., first and second stages) of the total process.

Recapitulating and summarizing, the operation of the system shown inFIGURE 10 is as follows: Master switch 7 0 is closed, which starts themotor 92 and applies voltage to the energizing leads 7% and 8t). Switch64 is closed for energizing the electromagnet 58 in order to hold a workpiece W on the lower end of the rack 22 with the rack in its elevatedposition. Heating lamp 49 is energized by closure of switch 66 in orderto preheat the electrolyte surface. Downward movement of the rack andthereby of the work piece into the cell, attended by application ofinitial electrolyzing voltage between the work piece W and opposingelectrode 12, is initiated by pressing the push-button switch 84, whichenergizes relay 67 and thereby energizes motor control relay 71. Themotor 52 is thereby energized and the exciter field circuit switch 670is thereby closed. Even though switch 84 is pressed momentarily, aholding circuit comprising relay switch e741 and timer switch 73amaintains energizetion of the relay 67. While the work piece W is beinglowered at a predetermined rate (established by the setting ofresistance 62), electrolyzing voltage is being generated and applied asdescribed.

When the work piece is lowered to the desired limit in the electrolyte,the arm or dog 58 closes the limit switch 54, which energizes relay 72and they deenergizes relay 71 by opening of relay switch 72a to stop themotor 52. It also closes relay switch 72b which by-passes resistance andthereby results in application of full heating voltage by the generator90 to the cell. Timer 73 is then actuated, by reason of closure ofswitch 54, which initiates the heating period. At the end of the heatingperiod, the timer switches are actuated into the reverse positions fromthose shown in the figure, so as to deenergize the electromagnet 5t) andthereby permit the work piece to drop down into the cell for coolingpurposes. Also, attendant opening of timer switch 73a results indeenergization of relay 67 and thereby termination of voltageapplication by generator 90 to the cell. Attendant closure of timerswitch 73b energizes relay 74 which forms a reversing circuit for therack motor 52, i.e., through closure of switches 74b and 74c. At thesame time, a holding circuit for relay 74 is formed through closure ofits switch 74a, so as to permit the motor 52 to raise the rack andthereby the electromagnet to the upper limit position. When the upperlimit position is reached switch 56 is opened, thereby deenergizingrelay 74 and terminating energization of the motor 52. The

s system is now prepared for a succeeding cycle of operation.

FIGURES 11 and 12 illustrate another application of the invention andcertain additional aspects thereof. In this case, the work piece Wacomprises a gear or other annular rotatable article, which is mounted ona suitable horizontal supporting shaft 1% carried by a hinged arm 1%.The arm is mounted on a pivot shaft lltl inter mediate its ends forraising and lowering the gear in relation to the electrolyte E in thecontainer it The negative terminal of direct-voltage source 112 isconnected to the arm 188 and thereby to the gear Wa to be heat treated,whereas the positive terminal of this source is connected to the linerelectrode 12 of container 1%. The gear Wat is slowly rotated by a speedreduction drive 11.4 acting through a belt 116 and pulleys 118 and 12%as shown.

A topping liquid I of an electrical and thermal insulating nature and ofa lower specific density than the electrolyte (i.e. such as transformeroil, water glass, kerosene, etc.) is maintained on the surface of theelectrolyte and is preferably of a depth which will cover a sufficientupper portion of the gear for cooling the latter as it emerges from theelectrolyte E. Thus, as the gear slowly rotates, the lower portionthereof immersed in the electrolyte undergoes the process of heatingheretofore described, whereas the upper portion thereof is immediatelyand continuously cooled in the cooler layer of topping liquid I. Ifdesired, the topping liquid 1 and, for that matter, also the electrolyteE may be kept at a desired temperature through suitable control means ofconventional or other type The layer insulating liquid I also serves toprevent the electrolyte from evaporating and to contain heat in theelectrolyte.

Consequently, by means of the apparatus shown in FiGURES 11 and 12,rotatable articles may be heated and cooled for heat treatment purposesin a single operation, that is, simultaneously.

FIGURES l3 and 14- illustrate a variation on the principle shown inFEGURES 11 and 12. In this case, a number of work pieces Wb are heattreated in direct succession by advancing them progressively firstthrough the topping liquid 1 and into the electrolyte E for heatingpurposes, and then back out through the topping liquid I for coolingpurposes. Parts which correspond to those in preceding figures bearsimilar reference numerals.

T he individual work pieces Wb are suspended on conductive metal hooksor the like 122 on a conductive rope, chain or cable, ets., 1'24, whichis guided by pulleys 126 and moved endwise of itself in an endlesscircuit by means of the drive motor unit 128. As the conductive cablemoves over the tank id it droops and permits the work pieces WI) whichis supports to move in a path which clips through the two layers ofliquid for purposes of achieving the desired successive heating andcooling operations. The supporting cable 124, being conductive, servesas a conductor of electricity to connect the negative side of thedirect-voltage source 112 to the work pieces Wb, whereas the positiveside of the source 112 is connected to the liner electrode 12 as shown.

In the embodiment shown in FIGURE arrangements are made forthermoforging of a work piece We in a heating cell comprising theelectrolyte container 10, the electrode 12, the heating lamp theelectrolyte E and the direct-voltage source 112 connected in the mannerindicated to the work piece support and to the liner electrode. The workpiece is supported on a vertically reciprocative hydraulic jack T36which comprises a cylinder 13%, a piston 13% and a piston rod lfstlchaving its lower end adapted to support the work piece. In line with thejack and mounted on the bottom of the electrolyte tank to, electricallyseparate from the liner electrode 12, i a mold or die I132 which isshaped to the desired conformation for the finished work piece. A sourceof pressurized hydraulic iiuid 134, is connected to the hydraulic jackcylinder in the manner indicated and is controlled by suitable means(not shown) the work piece in relation to the tank lit The hydraulicjack is supported by suitabe structural columns 136 and a rigid bridgingmember 138 interconnecting the upper ends of these columns, whereas thetank 1% and thereby the die T32 is supported by a lower bridging member140 interconnected to the lower ends of the columns 1%. The resultantstructure has sufficient mechanical strength to withstand the reactiveforces of the hydraulic jack pressing the Work piece We into the die 132for molding purposes.

Initially the work piece We is suspended in the electrolyte E byappropriate posi ning of the hydraulic piston 13%;) within the cylinder13%, and heating voltage from source ll is applied to the work piece andthe liner electrode 12. When the work piece reaches the desired workingtemperature, the hydraulic jack is actuated in order to press the workpiece forcibly against the die 132. The heating voltage may bediscontinued or continued as required in order to complete thethermo-forging operation. Repeated Withdrawals and heating followed byapplications to the die may or may not be necessary depending upon theextent of metal displacement required in the end result.

In the embodiment shown in FIGURE 16 a surgical instrument or othersmall metal tool or OiACl article Na is mounted in a metal holder 144having an insulated covering handle L26 adapted to be grasped in thehand H and to be suspended thereby in the electrolyte E within container15 with the liner electrode 12 connected to the positive side of thedirect-voltage source M2. The holder lid-4, and thereby the work pieceVVcl, is connected to the negative side of the source. By immersion ofthe Work piece Wd in the electrolyte with the voltage from source 1112applied in the manner indicated, the work piece soon becomes heated to atemperature (above C.) sufficient to kill all bacteria and may then becooled in the electrolyte E simply by disconnecting the direct-voltagesource (through a switch not shown) preparatory to performing thesurgical operation or other proces requiring a disinfected andsterilized instrument. if desired, the cooling may take place in air, sothat contamination from the electrolyte need not represent a problem. Ofcourse, if cooling is to occur in the electrolyte, the electrolyteshould be totally disinfected initially.

Referring to FIGURE 17, a technique and apparatus are disclosed formanufacturing alloy metal using two or more constituent metals. in thiscase, the different constituent metals Ml and M2 are fed in the form ofrods down into the electrolyte E in a position overlying the moldingcrucible 1 53. In this instance, the direct-voltage source 112'comprises a source 112's: having its negative terminal connected to therod M2, 21 separate sourc 112'!) having its negative terminal connectedto the rod Ml and a source tree having its negative terminal connectedto the crucible. The voltage of source 112's! and llZ'b may or may notbe the same. Usually they will ditler from each other, however, becauseof differences in melting temperatures of the component metals andbecause of a desire to control, by rate of melting, the relativepercentage of metals in the final alloy. The vol age of source llil'c ischosen to be just suflicient to keep the alloyed metals in the moltenstate for purposes of removal or handling, as well as uniform admixture.The positive terminals of the three separate sources within the source112 are connected to the liner electrode 12. The rods M1 and M2 are fedprogressively into the bath and melted at the required relative rat suntil the desired quantity of each metal has been reduced to molten formby the heating process and mixed with the other metal in the commoncrucible. The rate of mechanical feed of the two rods ultimatelycontrols the alloy ratio. Obviously, additional metals may also beincorporated at the same time and in the same manner.

It will therefore be seen that the invention has a number ofapplications and ramifications and that the illustrative embodimentsthereof represent new and useful teachings in the art of heating bymeans of electrolytic action in the initial stage followed bygaseous-electric discharge in the final or stabilized heating stage. Itwill also be seen that the process furnishes a novel and more highlyetheient means for heat treatment as well as other heating applicationsof metal out of contact with air, and it will be recognized by thoseskilled in the art that the invention has a number of modifications andvariations within the scope of the novel concepts involved.

I claim as my invention:

1. In an electric discharge heat-treatment process wherein a metal Workpiece is immersed in an electrolyte and an electric current is passedthrough the electrolyte with the work piece as one electrode, at asuiilcient voltage and for a sufficient time period to produce, in thelatter stage of said process, gaseous-electric discharge heating throughthe gaseous blanket generated electrolytically and by volatilization atthe work piece surface in the initial stages of said process, andthereafter terminating the current flow and allowing the work piece tocool in the electrolyte, the step of locally heating the surface layerof the electrolyte while maintaining the underlying electrolyte at asubstantially lower temperature, and lowering the work piece graduallyinto the electrolyte through the surface layer thereof while passingcurrent through the electrolyte with the work piece as an electrode togenerate a layer of gas at the electrode surface without heating theelectrode to a temperature higher than that produced in the latter stageof the process.

2. The process defined in claim 1, wherein the electrolyte surface ispreliminarily heated by directing radiant heat against the same in thearea through which the work piece is to be immersed.

3. The process defined in claim 1, wherein electrolyte from the body ofelectrolyte in which the heating is done is drawn off therefrom at alevel beneath the heated surface layer, is passed through an externalcooling circuit and is returned at a level substantially lower than saidfirst-mentioned level.

4. In an electric discharge heating apparatus, a container forelectrolyte, a first electrode in contact with electrolyte in saidcontainer, work piece supporting means to position a work piece immersedin the electrolyte, a

voltage source connected for applying voltage between said electrode andsaid work piece, heating means positioned adjacent the surface of theelectrolyte for heating the surface layer thereof to a temperaturesubstantially above the underlying electrolyte, means including saidsupporting means operable for progressively lowering the work piece intothe electrolyte with the source voltage applied, thereby to form agaseous film electrolytically and by volatilization at the work piecesurface, and means operatively associated with the voltage source forincreasing said applied voltage to produce gaseous-electric dis chargeheating of the work piece with the work piece immersed in a selectedposition in said container.

5. The electric discharge apparatus as in claim 4, wherein the workpiece supporting means comprises a meltable metal element also immersedin the electrolyte with the Work piece immersed in said selectedposition, and subjected to melting and thereby disconnecting the workpiece for dropping free in the electrolyte for cooling purposes afterpredetermined heating of the work piece therein.

6. The electric discharge apparatus as in claim 4, wherein the workpiece supporting means comprises electromagnet means adapted whenenergized for supporting the work piece positioned in the electrolyte,and means connected to the electromagnet for energizing the same for apredetermined heating period and for terminating such energization atthe end of such period.

7. The electric discharge apparatus defined in claim 4, furthercharacterized by electrolyte cooling means including means forcirculating the body of electrolyte which lies generally below saidsurface layer through said cooling means for maintaining said body ofelectrolyte at work piece cooling temperature.

8. In electric discharge heat-treatment apparatus, a container ofelectrolyte, positioning means for releasably suporting a work piece andfor lowering the same progressively into the electrolyte, a firstelectrode in contact with the electrolyte, a voltage source havingterminals connected respectively to said first electrode and to the workpiece, said voltage source having a pre-determined initial electrolyzingvoltage and being operable to produce an increased heating voltage,means for operating said positioning means to lower the work piece intothe electrolyte with said electrolyzing voltage applied, a lower limitswitch aetuatable in response to predetermined positioning of thelowered work piece, a timer connected to be actuated by said limitswitch for initiating a timed heating period, means connecting saidtimer to the voltage source to apply heating voltage to the work pieceduring said heating period, means connecting said limit switch to saidpositioning means to terminate lowering movement of the latter withactuation of said timer, means connected to be controlled by the timerupon termination of its timing period to operate the positioning meansin the reverse direction and to remove the applied voltage, and furthermeans connected to be controlled by the timer upon termination of itstiming period to actuate the positioning means for releasing the workpiece, whereby the latter drops into the electrolyte for coolingpurposes while the positioning means rises for a succeeding cycle ofoperation.

its?) References Cited by the Examiner UNITED STATES PATENTS 852,7325/07 Luthy 219-71 2,057,274 10/36 Mayhew 2l97l 2,953,672 9/60 Wisken etal 219-71 FOREIGN PATENTS 7,226 4/92 Great Britain.

OTHER REFERENCES Electrical Review, June 10, 1893, page 209.

DAVID L. RECK, Primary Examiner,

1. IN AN ELECTRIC DISCHARGE HEAT-TREATMENT PROCESS WHEREIN A METAL WORK PIECE IS IMMERSED IN AN ELECTROLYTE AND AN ELECTRIC CURRENT IS PASSED THROUGH THE ELECTROLYTE WITH THE WORK PIECE AS ONE ELECTRODE, AT A SUFFICIENT VOLTAGE AND FOR A SUFFICIENT TIME PERIOD TO PRODUCE, IN THE LATTER STAGE OF SAID PROCESS, GASEOUS-ELECTRIC DISCHARGE HEATING THROUGH THE GASEOUS BLANKET GENERATED ELECTROLYTICALLY AND BY VOLATILIZATION AT THE WORK PIECE SURFACE IN THE INITIAL STAGES OF SAID PROCESS, AND THEREAFTER TERMINATING THE CURRENT FLOW AND ALLOWING THE WORK PIECE TO COOL IN THE ELECTROLYTE, THE STEP LOCALLY HEATING THE SURFACE LAYER OF THE ELECTROLYTE WHILE MAINTAINING THE UNDERLYING ELECTROLYTE AT A SUBSTANTIALLY LOWER TEMPERATURE, AND LOWERING THE WORK PIECE GRADUALLY INTO THE ELECTROLYTE THROUGH THE SURFACE LAYER THEREOF WHILE PASSING CURRENT THROUGH THE ELECTROLYTE WITH THE WORK PIECE AS AN ELECTRODE TO GENERATE A LAYER OF GAS AT THE ELECTRODE SURFACE WITHOUT HEATING THE ELECTRODE TO A TEMPERATURE HIGHER THAN THAT PRODUCED IN THE LATTER STAGE OF THE PROCESS. 